Skip clear when writes masked

TRAC #12157
Signed-off-by: Shannon Woods
Signed-off-by: Daniel Koch

Author:    Nicolas Capens

git-svn-id: https://angleproject.googlecode.com/svn/trunk@232 736b8ea6-26fd-11df-bfd4-992fa37f6226

src/libGLESv2/Context.cpp

@@ -2164,7 +2164,7 @@ void Context::clear(GLbitfield mask)
             device->Clear(0, NULL, D3DCLEAR_ZBUFFER, color, depth, stencil);
         }
     }
-    else
+    else if (flags)
     {
         device->Clear(0, NULL, flags, color, depth, stencil);
     }